中华放射医学与防护杂志

朱志鹏,黎桂华,李相德,等.多叶准直器位置系统误差对不同T分期鼻咽癌容积旋转调强放疗计划的剂量影响研究[J].中华放射医学与防护杂志,2024,44(11):953-959.Zhu Zhipeng,Li Guihua,Li Xiangde,et al.Comparison of dosimetric impacts of the systematic errors of a multi-leaf collimator on volumetric modulated arc therapy plans for different T stages of nasopharyngeal carcinoma[J].Chin J Radiol Med Prot,2024,44(11):953-959

多叶准直器位置系统误差对不同T分期鼻咽癌容积旋转调强放疗计划的剂量影响研究

Comparison of dosimetric impacts of the systematic errors of a multi-leaf collimator on volumetric modulated arc therapy plans for different T stages of nasopharyngeal carcinoma

投稿时间：2024-03-25

DOI：10.3760/cma.j.cn112271-20240325-00100

中文关键词: 鼻咽癌容积旋转调强叶片位置异向系统误差剂量学

英文关键词:Nasopharyngeal carcinoma Volumetric modulated arc therapy Systematic error of multi-leaf collimator leaf position Dosimetry Complexity

基金项目:广西壮族自治区卫健委自筹课题(Z-A20230603,Z-A20230606)

作者	单位	E-mail
朱志鹏	广西医科大学第二附属医院放疗科, 南宁 530000
黎桂华	广西医科大学第二附属医院放疗科, 南宁 530000
李相德	广西医科大学第二附属医院放疗科, 南宁 530000
覃文	广西医科大学第一附属医院放疗科, 南宁 530012
郑莲容	广西医科大学第二附属医院放疗科, 南宁 530000	845150703@qq.com

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中文摘要:

目的研究多叶准直器(MLC)叶片位置系统误差对不同T分期鼻咽癌容积旋转调强放疗(VMAT)的剂量学影响。方法选取44例T_1~4N₁M₀鼻咽癌患者,在Pinnacle计划系统设计VMAT计划并作为初始计划,其中T₁和T₂期患者的计划原发肿瘤靶区(PGTV)处方剂量为68~70 Gy/33次,T₃和T₄期患者PGTV处方剂量为71 Gy/33次,其余计划靶区处方剂量相同。初始计划文件中,每个MLC叶片位置分别引入±0.2~±1 mm系统误差,使子野面积增大或减少,模拟VMAT治疗中MLC位置可能出现的误差计划。剂量评价指标分为靶区和危及器官,靶区为PGTV和PGTVnd的D_98%,危及器官为脑干、脊髓和视交叉的D_{0.1 cm³}。结果引入MLC位置系统误差后计划各剂量指标敏感度范围为(3.87%~9.87%)/mm(R²=0.932~0.998,P<0.01)。T₄期PGTV D_98%敏感度大于T₁、T₂和T₃期(Z=-3.12、-2.86、-2.59,P0.05),T₃期视交叉D_{0.1 cm³}敏感度小于T₁和T₂期(Z=-2.92、-2.72,P<0.05),T₄期视交叉D_{0.1 cm³}敏感度小于T₁和T₂期(Z=-3.51、-3.25,P<0.05)。跳数与单次PGTV处方剂量比(MU/Gy)和PGTV D_98%敏感度两者关系式为:y=-3.020+0.025x(r=0.80,P<0.05)。结论随着鼻咽癌T分期增大,计划的MU/Gy也随之增大,PGTV D_98%受MLC位置系统误差影响更大。T₄期鼻咽癌VMAT计划引入MLC位置系统误差后剂量变化普遍大于其他T期患者,需对T₄期鼻咽癌患者进行更严格的叶片位置质量控制,建议叶片系统误差小于0.42 mm。

英文摘要:

Objective To investigate the differences in dosimetric impacts of the systematic errors induced by the leaf positions of a multi-leaf collimator (MLC) on the volumetric modulated arc therapy (VMAT) for patients with different T stages of nasopharyngeal carcinoma (NPC). Methods A total of 44 patients with T_1-4N₁M₀ NPC were selected to design the VMAT plans using the Pinnacle planning system as the initial plans. The prescribed doses to the primary gross tumor volume (PGTV) were 68-70 Gy in 33 fractions for patients with T₁ and T₂ stage NPC and 71 Gy in 33 fractions for patients with T₃ and T₄ stage NPC. The prescribed doses to other target volumes were identical. In the initial plan files, a systematic error ranging from ±0.2 to ±1 mm was introduced to the position of each MLC leaf, leading to an increase or decrease in the subfield area. Then, potential error plans at the positions of MLC leaves during VMAT treatment were simulated. Dose evaluation indices involved target volumes and organs at risk (OARs). The indices related to target volumes consisted of the D98% of PGTV and PGTVnd, while those concerning OARs included the D_{0.1 cm³} of the brainstem, spinal cord, and optic chiasm. Results After the systematic errors induced by the positions of MLC leaves were introduced, the sensitivity range of each dose index range was (3.87%- 9.87%)/mm (R² = 0.932-0.998, P < 0.01). Specifically, patients with stage T₄ NPC displayed higher sensitivity to the D_98% of PGTV than those with stage T₁, T₂ and T₃ NPC (Z = -3.12, -2.86, -2.59, P < 0.05), patients with stage T₃ NPC exhibited lower sensitivity to the D_{0.1 cm³} of optic chiasm than those with stage T₁ and T₂ NPC (Z = -2.92, -2.72, P < 0.05), and patients with stage T₄ NPC manifested lower sensitivity to the D_{0.1 cm³} of chiasma than those with stage T₁ and T₂ NPC (Z = -3.51, -3.25, P < 0.05). The relationship between the sensitivity of MU/Gy and PGTV D_98% was y=-3.020+0.025x (r = 0.80, P < 0.05). Conclusion The MU/Gy in the plans increased with the T stage of NPC, and the D_98% of PGTV was more significantly affected by the systematic errors induced by the positions of MLC leaves. After the systematic errors induced by the positions of MLC leaves were introduced into the VMAT plans, doses to patients with T₄ stage NPC changed more significantly than those to patients with other T stages of NPC. Therefore, stricter quality control of leaf positions is required for patients with T₄ stage NPC, and it is recommended that the systematic errors should be less than 0.42 mm.

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